1. Field of the Invention
This invention relates to hose, and more particular relates to hose suitable for use in cryogenic applications.
2. Description of the Related Art
There are many systems for transporting fluids between an offshore structure such as a ship or other platform and an undersea pipeline. Examples of such systems include:                (1) The conventional multi-buoy mooring (CMBM) system. In this system a riser runs directly from the offshore structure down to the pipeline, with supporting buoys arranged at intervals along the length of the hose.        (2) The single tower mono-mooring (STM) system. In this system a mooring tower is fixed to the seabed and extends to the surface of the sea. The mooring tower supports a riser extending from the surface of the sea to the pipeline. A hose or other pipe can extend from the offshore structure and be connected to the end of the hose at the top of the mooring tower.        (3) The single anchor-leg mooring (SALM) system. In this system, a buoy is located close to the offshore structure, the buoy being attached to, and supporting, a connector unit located on or near the seabed. A riser extends from the offshore structure to the connecting unit, then from the connecting unit to the pipeline. A further section of pipe runs from the connector unit to the pipeline.        
(4) The catenary anchor-leg mooring (CALM) system. In this system, a buoy is located close to the offshore structure. A riser runs from the buoy to an underwater connector unit usually located on or near the seabed. A further section of pipe runs from the connector unit to the pipeline. A hose or other pipe can extend from the offshore structure and be connected to the end of the hose at the buoy. There are various configurations of the CALM system including the “Steep S” system, the “Lazy S” system and the “Chinese Lantern” system.
All the systems described above are well known in the art, and there are other possible systems that are not described above such as, for example, the use of an intermediate offshore structure. The essential feature of all these systems is that a riser is provided to deliver fluids from an offshore structure, such as a ship, to an underwater structure, such as a pipeline. The exact configuration of the riser, and of the support structure for the riser, can be varied depending prevailing conditions at the particular offshore location. Depending on the particular details of the system the riser comprises of submerged, floating and aerial sections.
There are also systems which involve the use of a submerged buoy, as described, for example, in WO96/36592. There are also systems involving the use of a vertically movable submerged buoy, such as those described in WO93/24731, and, more recently, in WO2006/044053 which essentially involves the use of the system described in WO93/24731 to transport cryogenic fluids.
All these types of system use rubber hose as the riser. A typical rubber hose has the following structure:                (1) A lining layer made of rubber.        (2) Multiple reinforcement layers of spirally applied high strength steel or polymeric reinforcing cords—these provide pressure and external load resistance.        (3) A helical steel wire outside the reinforcement layer, the helical wire being embedded within a rubber matrix.        (4) Further reinforcement layers of spirally applied high strength steel or polymeric reinforcing cords.        (5) A rubber cover.        
It will be appreciated that there are numerous variations of this structure such as the inclusion of a collapse resistant metallic carcass to increase the depth of submergence, an annulus to provide a double barrier between the internal fluids and the sea, material to provide buoyancy and insulation, and the build up of the outer cover to provide variable stiffness along the hose length so as to help prevent overbending.
Rubber hoses are usually classified as being of a bonded construction. A possible variation is to use conventional flexible pipe of unbonded construction, particularly in the submerged sections of the riser. A typical flexible pipe has the following structure:                (1) An inner stainless steel metallic carcass for collapse resistance.        (2) A lining layer made of a thermoplastic such as, for example, polyethylene or polyamide.        (3) Multiple reinforcement layers of spirally applied high strength steel wires—these provide pressure and external load resistance.        (4) An optional layer of spirally applied insulation.        (5) An outer cover made of a suitable thermoplastic material such as, for example, polyethylene or polyimide.        
The American Petroleum Institute's Recommended Practice For Flexible Pipe describes in some detail bonded and unbonded hose constructions and their use in the offshore environment.
Rubber hoses are very well suited to use in the systems described above, as they very tough and robust, and are known to be able to withstand the hostile conditions in which they are expected to operate. Rubber hoses are also flexible and are capable of being bent to small bend radii compared with their outer diameter. However, there is a problem with rubber hoses in that there is a limit on the lowest temperature at which they can operate effectively. For normal rubber, the lowest operating temperature is about −60° C. There are special rubbers available that can operate at temperatures down to about −100° C. However, rubber hoses cannot operate effectively at temperatures below about −100° C.
This means that rubber hoses are not suitable for applications which involve the transport of fluids at temperatures below about −100° C. In particular, such hoses are not suitable for the transportation of liquid natural gas (LNG), which typically requires the ability to operate at temperatures as low as about −162° C.
As noted above, WO 2006/044053 discloses a system for delivering cryogenic fluids from a ship to an underwater location using a system which utilises a vertically moving buoy. This patent envisages several possible types of riser for use with the system, in particular:                (1) The use of a conventional subsea pipe lined with a nickel alloy known as INVAR (registered trade mark).        (2) The use of a conventional cryogenic cargo hose structurally reinforced to resist hydrostatic forces.        (3) A pipe-in-pipe construction, which essentially involves the use of two concentric metal pipes.        (4) An arrangement of insulated hard pipe sections, the pipes typically being high nickel alloys, austenitic stainless steels and/or aluminium.        
However, this patent does not give any details about the specific construction of a working riser suitable for use in transporting cryogenic fluids below the surface of the sea. Furthermore, this patent relates in part to the transportation of non-cryogenic fluids having temperatures in the range of −28.9° C. to −100° C., which can be transported perfectly effectively with conventional rubber hose.
Other patents which relate to the problem of cryogenic subsea pipelines include EP1428748A1, GB2186657A, GB2408307A, U.S. Pat. No. 4,826,354A1 and WO2005/119150A2.
The construction of hose capable of carrying cryogenic fluids below the sea is a longstanding technical problem. Although patents, such the ones mentioned above, disclose solutions to the problem in general terms, in practice there are no commercially available solutions, owing to the difficulty and costs associated with the construction of the riser.